In case you missed it, major professional societies in critical care now strongly recommend prone positioning for patients with severe acute respiratory distress syndrome (ARDS), with a PaO2-to-FiO2 (P/F) ratio of ≤ 100. The recommendation marks a major shift in advised care for ARDS. Prone positioning improves ventilation-perfusion matching (transferring delivered oxygen into the bloodstream more [… read more]
Jon-Emile S. Kenny MD [@heart_lung] “Upward, not northward.” -E. A. Abbott A pressure chamber within a pressure chamber; the heart within the thorax. These are two pumps beating in-and-out of time, varying in physiology and pathophysiology between patients and within any one patient during the arc of an illness. As such, when we inspect the [… read more]
Jon-Emile S. Kenny MD [@heart_lung] -What is the world record for longest breath hold? -Why does the diagnosis of brain death require a rise in PaCO2 to at least 60 mmHg? -What minute ventilation can a human achieve? -What’s the difference between an elevated PaCO2 in someone who ‘won’t’ versus ‘can’t’ breathe? I’d like to [… read more]
Jon-Emile S. Kenny MD [@heart_lung] “To believe in medicine would be the height of folly, if not to believe in it were not a greater folly still.” -Proust A 32 year old man with no past medical history save for a BMI of 51 is admitted with severe acute pancreatitis following a large intake of [… read more]
Jon-Emile S. Kenny MD [@heart_lung] That high flow oxygen applied via nasal cannula lends itself to treating hypoxemic respiratory failure may be obvious. With adequate heat and humidification, oxygen can be employed relatively comfortably at very high flow rates – upwards of 60 L/min – to the nares. At such rates, the effort of the [… read more]
Jon-Emile S. Kenny MD [@heart_lung] with illustrations by Carla M. Canepa MD “Our life consists partly in madness, partly in wisdom: whoever writes about it merely respectfully and by rule leaves more than half of it behind.” -Montaigne Marking the 50 year anniversary of the first description of the adult respiratory distress syndrome – later [… read more]
In acute respiratory distress syndrome (ARDS), anyone with the keys to a ventilator knows low tidal volume ventilation (~6 mL/kg ideal body weight) is standard care. Low tidal volume ventilation can prevent or ameliorate ventilator-associated lung injury ; if early clinical trials represent current reality, one in 11 people with ARDS treated by low tidal volume ventilation could have their [… read more]
Jon-Emile S. Kenny MD [@heart_lung] Of the countless things taught to me by Dr. Chitkara at the Palo Alto VA Health Care System, one that sticks is the difference between density-dependent and viscosity-dependent airflow. He often used the chronic bronchitic suffering through the viscous, humid New York City summers as a teaching example. The importance [… read more]
By Jon-Emile S. Kenny [@heart_lung] When interpreting hemodynamic studies of drugs which – potentially – alter the resistance of the pulmonary vascular tree, we often turn to the calculated pulmonary vascular resistance [cPVR] as our guide. For instance, a vasopressor determined to increase the cPVR is wholly avoided in a patient with pulmonary arterial hypertension. We [… read more]
Jon-Emile S. Kenny [@heart_lung] “Doctrine once sown strikes deep its root, and respect for antiquity influences all men.” -William Harvey [1628] The use of hyperoncotic albumin to draw fluid from the interstitial space permeates dark corners of the critical care community. The ‘pull and push’ of 25% albumin followed by furosemide remains somewhat of a [… read more]
Jon-Emile S. Kenny [@heart_lung] While parts 1 and 2 of this trilogy considered the mechanical power applied to the lung skeleton and the effects of lung inhomogeneity [i.e. ‘stress raisers’], respectively; this final installment will draw the reader towards the pulmonary vasculature as a key mediator of ventilator induced lung injury [VILI]. That the pulmonary [… read more]
Jon-Emile S. Kenny [@heart_lung] Gattinoni and Quintel have, very recently, outlined their approach to managing the acute respiratory distress syndrome [ARDS] [1]. They argue that treatment of ARDS should minimize firstly, the mechanical power applied to the lungs – as described in part 1. Secondly, Gattinoni and Quintel note that, in the treatment of ARDS, [… read more]
Jon-Emile S. Kenny [@heart_lung] “Often, as new knowledge progresses, old knowledge is abandoned or forgotten.” -Luciano Gattinoni In a succinct and current treatise, Gattinoni and Quintel outline the modern management of the acute respiratory distress syndrome [ARDS] [1]. It is imperative, they reason, that treatment of ARDS minimizes firstly, the mechanical power applied to the [… read more]
Jon-Emile S. Kenny [@heart_lung] In part 2, I continue my commentary on this excellent review; part 1 may be found here. In this post I will consider patients with severe metabolic acidosis and those with right ventricular [RV] dysfunction and/or failure. Severe Metabolic Acidosis In patients with severe metabolic acidosis, alveolar ventilation tends to be maximal [… read more]
By Jon-Emile S. Kenny [@heart_lung] The problem with the lung in the acute respiratory distress syndrome [ARDS] is not that it is stiff, but rather, that it is small [1]. In the 1980s, CT scans of the lungs of patients with ARDS revealed that the functional lung was attenuated in size and that dependent densities [… read more]
ICU Physiology in 1,000 Words “The Hemodynamics of Prone” by Jon-Emile S. Kenny MD A physiological maelstrom has recently swirled about the hemodynamic effects of the prone position in severe ARDS [1-5]; but how exactly does this maneuver alter the cardiovascular system? A good approach to this problem is a Guytonian one whereby we consider [… read more]
Image: Rotoprone Acute respiratory distress syndrome (ARDS) injures the lungs in a heterogeneous pattern, and the damaged areas are particularly vulnerable to further ventilator-induced lung injury. This is why a lung-protective ventilator strategy using low tidal volumes reduces mortality from ARDS, experts believe. Tidal volumes of 6 mL/kg ideal body weight (calculated from height) using conventional [… read more]
Image: Dartmouth Nitric Oxide: No Benefit Even in Severe ARDS Giving inhaled nitric oxide to people with acute respiratory distress syndrome (ARDS) improves oxygenation, but has never been demonstrated to improve survival. Not many physicians seem to use nitric oxide for ARDS anymore, except possibly as salvage therapy in life-threatening refractory disease. Even that well-meaning [… read more]
Prevention and Management of Ventilator-Induced Lung Injury See also Part 1: Mechanisms of Ventilator-Induced Lung Injury The recognition that lifesaving mechanical ventilation can also be harmful, even lethal, has led to a sea change in the use of mechanical ventilation in critically ill patients — at least in theory. For people with acute respiratory distress [… read more]
Mechanisms of Ventilator-Induced Lung Injury (Part 1) See also Part 2: Prevention and Management of Ventilator-Induced Lung Injury Although invasive mechanical ventilation saves tens of thousands of lives each year, it can also be harmful, causing or worsening acute respiratory distress syndrome (ARDS) when misapplied. The repetitive stretching of lung tissue during positive pressure ventilation [… read more]
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